Decarbonizing a direct injection engine (intake valves)

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﻿OVERALL DIFFICULTY INDEX: 6/10

IF YOU HAVE NO TOOLS YOU SPEND $ 200 TO GET THEM FOR THIS JOB

IF YOU HAVE NO EXPERIENCE YOU SPEND 10 HOURS TO CARRY OUT THIS JOB

RISK OF BURNS, SEE BELOW​

BEFORE YOU START

Work only on a cold engine to avoid any risk of burns.

The job is technically easy but it would be very difficult to reach the cylinder head inlets. This requires dismantling many hoses and bend over the engine for hours. Do not attempt to do so if you suffer from back or shoulder pain or injury.

Note: The below works occurred on a Peugeot 5008 equipped with an EP6 direct injection and turbocharged engine. Works remain similar for other engines.

DISCLAIMER:Our pictorials are of informative nature and do illustrate works carried out by ourselves at our own premises for our own use and satisfaction. Readers who envisage to carry out similar works inspired by the below method shall do this at their own risks and liability.

Carbon deposits on intake valves: causes and symptoms

In direct injection engines no fuel passes through the intake valves since the injection occurs downstream directly into the combustion chamber.

The gasoline vapors coming through the EVAP circuit are not enough to ensure some valve cleaning.

The engine oil that is recycled from the oil vapor breather makes the carbon deposits sticky enough for the valves to end up clogged. See facing picture : a brush introduced into the inlet of a cylinder head comes out completely covered with the sticky compound.

Symptoms:

Most common symptom is a difficulty to rev the engine beyond 3,000/4,000 rpm since no sufficient air gets in.

It does not trigger any DTC since the ECU will adapt and inject less fuel.

The engine works perfect on low rpm's and maintains a good torque.

Fuel consumption goes up. Not far from an additional 1.5l/100Km.

Cure:Unless you own a decarbonizing machine, the cure is purely mechanical at DIY level i.e. the carbon deposits are manually removed without dismantling the cylinder head using brushes, compressed air, a powerful vacuum, etc.

The tools

Start by buying all kinds of brushes that can go into the inlets of your cylinder heads and more or less around the valves.Use only metal or hard plastic brushes for domestic use.Anything abrasive (like sandpaper) is strictly prohibited.

It happens this grill cleaning brush fits perfectly well the job for the first layers of carbon since it provides two heads one for each valve of a cylinder!

The best brush that reaches far on each side of the valve rod was made out of the smallest metal wheel brush fitted on a hunting rifle cleaning rod (left). The brush of a 12-gauge hunting rifle is also efficient enough (right)

Important note: it is advised to rotate the brushes by hand only not to take the risk of having one stuck behind a valve rod which would make it impossible to remove without dismantling the cylinder head.

How to clean the inlet valves carbon deposits

Proceed cylinder by cylinder and per each type of brush used.Use a mirror and a torch light to see what's happening and how advanced you are in the cleaning process.

Then use a powerful vacuum cleaner to clear the deposits you have released.If you have compressed air, use it after the vacuum.

The smallest brush will do the most efficient work for the very last deposits.Alternate the rotation by hand while gently pushing on the rod to keep some pressure.

Once done, you can use any cleaner spray but do not put too much in there.Briefly spray once each valve.​Collect excess liquid on a towel (old socks) wrapped around a screwdriver:

The end result is not shown here due to the flash limitations making it impossible to take a picture inside and clearly show the valves.